Omp.h not found after fresh install with apt.llvm.org/llvm.sh (WSL2 Ubuntu 20.04)

Hi
I have a quite new Ubuntu 20.04 installed on WSL2. I have gcc-8 and gcc-9 (default) and want to use clang++. I used apt.llvm.org/llvm.sh, but fail to get a simple file containing #include <omp.h> to compile:

$ /usr/bin/clang-13 -fopenmp -v  -c /home/kris/devel/build
-clang13/builds/parallelproj/build/CMakeFiles/FindOpenMP/OpenMPTryFlag.c
Ubuntu clang version 13.0.1-++20211019123057+8a93745a7121-1~exp1~20211019003646.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Candidate multilib: .;@m64
Selected multilib: .;@m64
 (in-process)
 "/usr/lib/llvm-13/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -disable-llvm-verifier -discard-value-names -main-file-name OpenMPTryFlag.c -mrelocation-model static -mframe-pointer=all -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -v -fcoverage-compilation-dir=/home/kris/devel/build-clang13/builds/parallelproj/build -resource-dir /usr/lib/llvm-13/lib/clang/13.0.1 -internal-isystem /usr/lib/llvm-13/lib/clang/13.0.1/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdebug-compilation-dir=/home/kris/devel/build-clang13/builds/parallelproj/build -ferror-limit 19 -fopenmp -fgnuc-version=4.2.1 -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o OpenMPTryFlag.o -x c /home/kris/devel/build-clang13/builds/parallelproj/build/CMakeFiles/FindOpenMP/OpenMPTryFlag.c
clang -cc1 version 13.0.1 based upon LLVM 13.0.1 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/9/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/llvm-13/lib/clang/13.0.1/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
/home/kris/devel/build-clang13/builds/parallelproj/build/CMakeFiles/FindOpenMP/OpenMPTryFlag.c:2:10: fatal error: 'omp.h' file not found
#include <omp.h>
         ^~~~~~~
1 error generated.

Trying to find where it is:

$ locate omp.h|grep /omp.h
/mnt/c/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.29.30133/include/omp.h
/usr/lib/gcc/x86_64-linux-gnu/8/include/omp.h
/usr/lib/gcc/x86_64-linux-gnu/9/include/omp.h

I note that these include paths are not on the list above, but I have no idea if this is intentional or not.

Any suggestions?

This is fixed by

sudo apt install libomp-13-dev

Looks like a bug in llvm.sh to me…